1. Field of the Invention
The present invention relates generally to alarm systems for detecting leaks in fluid delivery lines and, more particularly, to an alarm system specifically adapted for application to and retrofitable with conventional bulk and fuel filling stations.
2. Description of the Prior Art
Prior fluid leak alarms have been primarily of a mechanical nature which are expensive, require extensive installation effort, and tend to restrict pump flow.
A more recent prior art approach by Reynolds in U.S. Pat. No. 3,935,567 attempts to overcome the above prior art problems. The Reynolds approach, as stated in the above-identified specification, comprises:
Three essential elements--a pressure-sensitive switch, a timing circuit which measures the lead-down in pressure of the line between the pump and the dispensing nozzle, and an indicator means responsive to either a leak or non-leak condition. If a predetermined drop in pressure is measured by the pressure-sensitive switch, a circuit is operated which turns on an indicator light, thereby visually indicating a defective or leaky system. If no leak is detected, a non-leak indicator light is turned on denoting that the system is satisfactory.
Unfortunately, the Reynolds approach is not truly retrofitable to existing filling stations. Reynolds relies upon two wires coming from each product line or dispenser, in which case the concrete must be disrupted to bury the wires beneath the ground or pulled through existing sealed conduits or in which case the wires coming from the dispenser to the gas station are above the ground but pose a hazard and reliability problem. With so many wires, another problem apparent in Reynolds is that the wires act as antennas and, therefore, excessive engine electrical noise, signals from CB transmitters, or other electrical interference can be picked up by the interconnecting wires and extended into the remote detector located in the filling station to trigger perhaps a false alarm. If the wires are placed above the ground a safety hazard may arise due to tripping or the like. Also, the wires, if above ground, may be severed or otherwise damaged. Furthermore, the Reynolds approach requires the use of two indicators per line.
More recent descriptive literature from Reynolds Engineering, 1251 W. Lehigh Pl., Englewood, Colo., discloses an improved alarm system over the above Reynolds patent. The descriptive literature, while not disclosing the electrical circuit, reduces the number of wires coming from each product line from two to one. Furthermore, provision is now made in the improved alarm system by Reynolds to indicate Premium, Regular, and Unleaded product lines in a single remote alarm package. The problems of installation costs, radiation pick-up, or safety, however, are not overcome by the improved Reynolds approach.
The present invention overcomes the difficulties presented by the above prior art approaches by providing, for the first time, the complete elimination of interconnecting wires between the remote alarm located in the filling station building, and the detectors located at the dispensers for each of the different product lines. The present invention utilizes the conventionally buried power line which delivers electrical power from the station to the dispensers for transmission of alarm signals. This approach eliminates the need for any separate interconnecting wires, and eliminates the need for tearing up or otherwise modifying the concrete or asphalt surface between the dispensers and the station.
Furthermore, this new and novel invention utilizes coded signaling techniques that provide for each product line a unique frequency modulated (FM) and amplitude modulated (AM) signal which is extended over the power line from the dispenser to the remote alarm. The use of such uniquely different codes prevents any false indications which may arise from ambient electrical noise such as automotive electrical noise, CB transmission interference, or any other electrical interference.
Furthermore, the present invention can detect leaks occurring in the fuel delivery line whenever fuel is being pumped and for a predetermined time after the pumping is deactivated. Prior art approaches do not provide such a comprehensive time span of testing.
In addition, the present invention can be tested daily to ensure proper working operation. When the attendant arrives to turn the various product lines on, he can verify the total integrity of the system. Prior art approaches do not provide such integrity double checks.
Also, since interconnecting wires are not used and conventional power delivery lines are used, the installation cost of the present invention is substantially lower than any of the above prior art approaches.
Finally, the present invention provides a fully portable remote alarm since the alarm can be plugged into any electrical outlet within the filling station building. This is highly desirable since the user can selectively reposition the alarm with a minimum of effort. None of the above prior art approaches contemplate such mobility or convenience to the user.